Design and method for the manufacture of polymer cartridge case rimfire small arms ammunition

ABSTRACT

A rimfire cartridge case may comprise a cylindrical case body, a case head disposed at a first end of the cylindrical case body, and a case mouth disposed at a second end of the cylindrical case body. The case head may have a circumference greater than a circumference of the cylindrical case body. The case head may comprise a hollow envelope configured to contain a priming mixture. The case mouth may be configured to mechanically engage a projectile. The cylindrical case body and the case head may be integrally formed in a single piece from a polymer material to define a chamber configured to hold a propellant and to contain a pressure generated by the propellant when the propellant is ignited by the priming mixture. Also disclosed are inventive engineered polymers for use in cartridges.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application No. 62/047,393, filed Sep. 8, 2014, which is hereby incorporated by reference in its entirety.

BACKGROUND

Standard rimfire ammunition cartridge cases are constructed from a metallic material (e.g., brass or steel) to give them strength to contain the chamber pressures generated when the ammunition is fired. Some metals used to produce small arms ammunition are produced using materials which are not environmentally safe or recyclable.

BRIEF SUMMARY OF THE INVENTION

An engineered polymer material rimfire small arms ammunition cartridge case and the method for manufacturing the same are described herein. The engineered polymer material may meet the Sporting Arms and Ammunition Manufacturers Institute (SAAMI) and/or Commission Internationale Permanente (CIP) specifications for the design of .22 caliber and other caliber rimfire small arms ammunition cartridges. The ballistic performance of the rimfire small arms ammunition using the described polymer case may meet the SAAMI ballistic performance standards. The cartridge case design may allow the projectile/bullet to snap into place during the loading process after the case is primed and powder is placed in the cartridge case. The rimfire cartridge case may be formed by injection molding or a blow molding process, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a polymer rimfire small arms ammunition cartridge case according to an embodiment of the invention.

FIG. 2 a shows a polymer rimfire small arms ammunition cartridge case fitted with a .22 caliber projectile/bullet according to an embodiment of the invention.

FIG. 2 b shows a .22 caliber projectile/bullet according to an embodiment of the invention.

FIG. 3 a shows a polymer rimfire small arms ammunition cartridge case with locking lip according to an embodiment of the invention.

FIG. 3 b shows a polymer rimfire small arms ammunition cartridge case with locking lip and .22 caliber projectile/bullet according to an embodiment of the invention.

FIG. 3 c shows a polymer rimfire small arms ammunition cartridge case with locking lip and .22 caliber projectile/bullet according to an embodiment of the invention.

FIG. 4 shows a polymer rimfire small arms ammunition cartridge case and .22 caliber projectile/bullet locked into a locking lip of the case according to an embodiment of the invention.

FIG. 5 a shows a polymer rimfire small arms ammunition cartridge case head according to an embodiment of the invention.

FIG. 5 b shows a polymer rimfire small arms ammunition cartridge case head according to an embodiment of the invention.

FIG. 5 c shows a polymer rimfire small arms ammunition cartridge case head according to an embodiment of the invention.

FIG. 6 a shows a polymer rimfire small arms ammunition cartridge case with locking lip according to an embodiment of the invention.

FIG. 6 b shows a projectile suitable for use with the cartridge case of FIG. 6 a.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

Rimfire cartridge cases described herein may be made of an engineered polymer comprising materials which make it strong enough to withstand the interior pressures created by firing any rimfire small arms cartridge case such as the .22 short, .22 long, .22 long rifle, .22 Magnum, .22 Stinger, .22WRF, 5mm Remington Magnum, .17 Hornady Magnum, or .17 Hornady Mach 2 caliber cartridge, or any other firearm using a rimfire firing mechanism to ignite the cartridge priming mixture and the propellant contained in the ammunition cartridge case. A polymer cartridge case may be manufactured to the design specifications of SAAMI and/or CIP to produce a fully loaded rimfire small arms ammunition cartridge (e.g., a conventionally loaded cartridge containing a small arms ammunition priming mixture, a small arms ammunition smokeless powder propellant, and a projectile/bullet).

FIG. 1 shows a polymer rimfire small arms ammunition cartridge case 1 according to an embodiment of the invention. The case 1 may include a case mouth 2, which may be an opening in the case 1, a cylindrical case body 3, and a case head 4, which may be a closed end of the body 3 configured to make contact with a firing pin of a gun when fired. The case head 4 may be flared and rounded to form an integral rim base, the circumference of which may be wider than the circumference of the upper cylindrical wall near the case mouth 2. As shown in FIG. 2 a, a .22 caliber projectile/bullet 5 may fit into the case mouth 2. Note that while the case 1 of FIG. 2 a is sized for use in a .22 long rifle cartridge, similar features may be found on cases for other types of rimfire ammunition. The dimensions in this and other figures are presented as example dimensions only. The case 1 may be sized for any rimfire small arms application, including, but not limited to, .22 short, .22 long, .22 long rifle, .22 Magnum, .22 Stinger, .22WRF, 5mm Remington Magnum, .17 Hornady Magnum, or .17 Hornady Mach 2 calibers. The case 1 may be configured for use in straight wall and/or bottleneck rimfire cartridge designs. The mouth 2 may receive a metered amount of propellant/powder to be housed within a volume of space inside of the case body 3 formed when the projectile/bullet 5 is installed. The flared, rounded bottom of the cartridge case 1 defined by the case head 4 may form a hollow envelope according to SAAMI design specifications to accept the priming material which is used to ignite the propellant/powder. As shown in FIG. 5 a, the hollow envelope 7 may be disposed near the rim of the case head 4. When the rim of the cartridge case head 4 is struck by the firing pin of a firearm, the priming mixture may ignite the propellant/powder, thus firing the projectile/bullet 5. FIG. 5 b shows an embodiment wherein a priming mixture wafer is disposed in the envelope 7 at the case head 4 circumference. FIG. 5 c shows an embodiment wherein a priming mixture fills the envelope 7 at the case head 4 circumference.

FIG. 3 a shows further details of a polymer rimfire cartridge case 1 according to an embodiment of the invention. A magnification of a cross section of the case body 3 in the area of the case mouth 2 is shown. The case body 3 may include a locking lip 6. The case body 3 may be molded in one piece with a locking lip 6 configuration molded into the case mouth 2. As shown in FIG. 2 b, a .22 caliber projectile/bullet 5 may include a groove 5 a which may be inserted into the case mouth 2. In metallic cases, the projectile/bullet 5 may be held in place using a crimping of the metallic case which is commonly known in the industry as a knife cut crimp. This knife cut crimp is used to bend the metallic case against the projectile/bullet 5 to lock the projectile/bullet in the case by bending the case into the groove 5 a. Thus, many .22 caliber projectile/bullets 5 available for use in metallic cases may also be used with the polymer cartridge case 1. As shown in FIGS. 3 b and 3 c, the locking lip 6 of the case body 3 may snap the polymer cartridge case 1 walls into the mating groove 5 a formed around the circumference of the projectile/bullet 5. The polymer of the case 1 may be sufficiently flexible to accept the projectile/bullet 5 when the projectile/bullet 5 end is pushed into the mouth 2 past the locking lip 6, but still rigid enough to contain combustion when the propellant/powder is ignited. The locking lip 6 may mate 6 a with the mating groove 5 b to hold the projectile/bullet 5 in place and ensure that the projectile/bullet is installed in a proper position so that the entire cartridge is sized according to the specifications of its caliber. As shown in FIG. 4, the locking lip 6 may cover the full circumference of the mouth 2 of the case 1 and may mate with the mating groove 5 a along the entire circumference of the projectile/bullet 5. Installing the projectile/bullet 5 into the case 1 may therefore form a chamber in which the propellant/powder for the cartridge may be held.

In some embodiments the projectile/bullet 5 can be held firmly in place within the case 1 with an adhesive such as a cyanoacrylate acrylic resin. A resin such as cyanoacrylate may be used to create a strong bond between the projectile/bullet 5 and the cylindrical wall 3 of the cartridge case mouth 2. Adhesive may be used in combination with the locking lip 6 so that the locking lip 6 can position the projectile/bullet 5 at a desired depth within the case 1 and the adhesive can secure the projectile/bullet 5.

FIGS. 6 a and 6 b show a polymer rimfire small arms ammunition cartridge case 100 (FIG. 6 a) and projectile 130 (FIG. 6 b) for use therewith according to another embodiment of the invention. The case 100 may include a case mouth 120, which may be an opening in the case 100, a cylindrical case body 110, and a case head 140, which may be a closed end of the body 110 configured to make contact with a firing pin of a gun when fired. The case head 140 may be flared and rounded to form an integral rim base, the circumference of which may be wider than the circumference of the upper cylindrical wall near the case mouth 120. A .22 caliber projectile/bullet 130, with a circumferential depression 136 configured to mate with locking lip 160 of the case body 110, may be inserted into the case mouth 120. The mouth 120 may receive a metered amount of propellant/powder to be housed within a volume of space inside of the case body 110 prior to installation of the projectile/bullet 130. The polymer of the case 100 may be sufficiently flexible to accept the projectile/bullet 130 when the projectile/bullet end 137 is pushed into the mouth 120 past the locking lip 160, but still rigid enough to contain combustion when the propellant/powder is ignited. The projectile 130 has an outside diameter D2 that is slightly smaller than the inner diameter D1 of a corresponding portion of the interior chamber 111 of the casing 100 to allow the projectile 130 to be inserted into the casing 100. The projectile endwall 137 may have a chamfered edge 138 to allow the endwall 137 of the projectile 130 to be inserted past the edge 161 of the locking lip 160 so that the circumferential depression 136 of the projectile can engage the locking lip 160 (i.e., the chamfered edge 138 will exert an outward force on the locking lip 160 such that the sidewall of the casing 100 will deform/expand to allow the endwall 137 of the projectile 130 to be pushed past the locking lip 160 to a point where the locking lip 160 mates with the channel 136 of the projectile 130). The flared, rounded bottom of the cartridge case 100 defined by the case head 140 may form a hollow envelope according to SAAMI design specifications to accept the priming material which is used to ignite the propellant/powder.

While the case 100 of FIG. 6 a is sized for use in a .22long rifle cartridge, similar features may be found on cases for other types of rimfire ammunition. The dimensions in this figure are presented as example dimensions only. The case 100 may be sized for any rimfire small arms application, including, but not limited to, .22 short, .22 long, .22 long rifle, .22 Magnum, .22 Stinger, .22WRF, 5 mm Remington Magnum, .17 Hornady Magnum, or .17 Hornady Mach 2 calibers. The case 100 may be configured for use in straight wall and/or bottleneck rimfire cartridge designs.

The cartridge cases discussed above may be formed of a polymer, preferably an engineered polymer which is either injection molded or injection blow molded. The engineered polymer may be formed of a nylon resin. Examples of such nylon resins include PA6, NYCOA 8330™ available from Nylon Corporation of America, and RTP 299DX140551™ (natural) from RTP Co. of Winona, Minn., In order to improve the thermal and mechanical properties of cartridge cases made from such nylon resins, various additives may be added. For example, in one embodiment, a nano-composite material comprises a nylon (PA6) base in which nano-clays which are members of the smectite class of layered silicate or platy minerals are dispersed. The nano-clays may include alumino-silicate particles which are uniformly dispersed in a polymer matrix. Another example of a suitable material may be formed from a NYCOA 8330™ base and carbon nanotube (CNT), basalt and/or silica nanoparticle additives. In one embodiment, either CNT, basalt or silica nanoparticle additives are present with weight percentages between 0.25-5, and more preferably 0.5, 1, 1.5 or 2 weight percent. Yet another example includes an RTP 299DX140551 base and additives comprising ball-milled ceramic fibers available from Thermal Products Co. of Norcross, Ga. or powdered KEVLAR™ fibers. Beads of such polymers may be molded into the cartridge case components discussed above using an injection molding or blow molding process. In some embodiments, the material flexibility is sufficient to allow the mouth of the cartridge case to accept a bullet/projectile with an annular groove engaged by a corresponding detent in the cartridge mouth.

Engineered polymers may save natural resources and may be more recyclable than metals. The nano-polymer variants combined to form the case may allow the pressures experienced by the case to equal and/or exceed the pressures experienced in the firing of conventional brass or steel cased .22 rimfire ammunition. The finished engineering polymer cartridge case may equal and/or exceed the ballistic performance of metallic .22 rimfire casings. The nano-composites and/or other materials discussed above may provide the cartridge case with high stiffness which may be comparable to metallic materials. This may provide the ability to produce thin walls and light weight ammunition. Engineering polymers may provide favorable reaction to high heat distortion temperatures and high retention of mechanical properties under humid conditions. Nano-composites and/or other materials discussed above may make the case material inherently fire retardant. Additionally, polymers used for the case may have explosive/propellant compatibility and may prevent moisture absorption while providing moisture protection given to the complete round of ammunition.

While various embodiments have been described above, it should be understood that they have been presented by way of example and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope. In fact, after reading the above description, it will be apparent to one skilled in the relevant art(s) how to implement alternative embodiments.

In addition, it should be understood that any figures which highlight the functionality and advantages are presented for example purposes only. The disclosed methodology and system are each sufficiently flexible and configurable such that they may be utilized in ways other than that shown.

Although the term “at least one” may often be used in the specification, claims and drawings, the terms “a”, “an”, “the”, “said”, etc. also signify “at least one” or “the at least one” in the specification, claims and drawings.

Finally, it is the applicant's intent that only claims that include the express language “means for” or “step for” be interpreted under 35 U.S.C. 112 (f). Claims that do not expressly include the phrase “means for” or “step for” are not to be interpreted under 35 U.S.C. 112 (f). 

We claim:
 1. A rimfire cartridge case comprising: a cylindrical case body; a case head disposed at a first end of the cylindrical case body and having a circumference greater than a circumference of the cylindrical case body, the case head comprising a hollow envelope configured to contain a priming mixture; and a case mouth disposed at a second end of the cylindrical case body and configured to mechanically engage a projectile; wherein the cylindrical case body and the case head are integrally formed in a single piece from a polymer material to define a chamber configured to hold a propellant and to contain a pressure generated by the propellant when the propellant is ignited by the priming mixture.
 2. A rimfire cartridge comprising: the rimfire cartridge case of claim 1; the projectile disposed in the case mouth; the propellant disposed in the chamber; and the priming mixture disposed in the hollow envelope.
 3. The rimfire cartridge case of claim 1, wherein the cylindrical case body comprises a locking lip disposed on an inner surface of the cylindrical case body at the case mouth, the locking lip being configured to mate with a mating groove of the projectile.
 4. The rimfire cartridge case of claim 1, further comprising an adhesive disposed on an inner surface of the cylindrical case body at the case mouth.
 5. The rimfire cartridge case of claim 1, wherein the polymer material comprises a nano-composite material comprising a nylon base.
 6. The rimfire cartridge case of claim 1, wherein the polymer material is formed by polymerization of a nano-clay which is a member of the smectite class of layered silicate or platy minerals.
 7. The rimfire cartridge case of claim 6, wherein the nano-clay comprises alumino-silicate particles uniformly dispersed in a polymer matrix.
 8. The rimfire cartridge case of claim 1, wherein the single piece comprising the cylindrical case body and the case head is formed in an injection molding or a blow molding process.
 9. The rimfire cartridge case of claim 1, wherein the priming mixture comprises a wafer inserted in the hollow envelope.
 10. The rimfire cartridge case of claim 1, wherein the cartridge case meets or exceeds the Sporting Arms and Ammunition Manufacturers Institute (SAAMI) specifications for the design of rimfire small arms ammunition cartridges.
 11. The rimfire cartridge case of claim 1, wherein the cartridge case meets or exceeds the Commission Internationale Permanente (CIP) specifications for the design of rimfire small arms ammunition cartridges.
 12. The rimfire cartridge case of claim 1, wherein the cartridge case is configured to be used for .22 short, .22 long, .22 long rifle, .22 Magnum, .22 Stinger, .22WRF, 5mm Remington Magnum, .17 Hornady Magnum, or .17 Hornady Mach 2 caliber ammunition.
 13. The rimfire cartridge case of claim 1, wherein the cylindrical case body is a straight walled cylinder.
 14. The rimfire cartridge case of claim 1, wherein the cylindrical case body includes a bottleneck. 